cmake _HAVE__FLOAT16 examples

HDFGroup/hdf5 config/ConfigureChecks.cmake :1112 

unset (${HDF_PREFIX}_HAVE__FLOAT16 CACHE)

InsightSoftwareConsortium/ITK Modules/ThirdParty/HDF5/src/itkhdf5/config/cmake/ConfigureChecks.cmake :1005 

unset (${HDF_PREFIX}_HAVE__FLOAT16 CACHE)